1. Field of the Invention
The present invention relates to a laser diode module applicable to an optical fiber communication system.
2. Description of the Related Art
In a general optical communication system to which intensity modulation/direct detection (IM/DD) is applied, the light output power of a laser diode (LD) changes with an injection current. On the basis of this characteristic modulation current pulses are applied to the LD current-biased in the vicinity of an oscillation threshold to obtain light whose intensity is modulated. The I-L characteristic of the LD (the characteristic representing the relation between the injection current and the light output power of the LD) is dependent upon temperature and changes with a temperature change. It is therefore desirable to control the temperature of the LD to a constant value in order to obtain a constant operation condition irrespective of an ambient temperature.
Conventionally known is a laser diode module having a housing, a thermoelectric cooling element provided in the housing, a base provided on the thermoelectric cooling element, and an LD mounted through a laser carrier on the base. Further, thermistor is usually mounted by a thermistor carrier on the base,""so as to detect a temperature in the vicinity of the LD in the module. The thermistor is connected to a terminal for external connection of the module by a bonding wire formed of gold, for example.
As the gold bonding wire has a good thermal conductivity, a temperature difference between the inside and the outside of the module causes heat flow from the outside through the terminal and the bonding wire to the thermistor, or heat flow from the thermistor through the bonding wire and the terminal Lo the outside, so that high-precision temperature control cannot be performed. For example, when the temperature outside the module becomes relatively high, heat flows from the outside through the terminal and the bonding wire to the thermistor, so that the temperature of the thermistor becomes higher than that of the LD. Conversely, when the temperature outside the module becomes relatively low, heat flows from the thermistor through the bonding wire and the terminal to the outside, so that the temperature of the thermistor becomes lower than that of the LD. The I-L characteristic changes with such a temperature difference between the thermistor and the LD, causing a change in oscillation threshold Ith of the LD to an unignorable degree (e.g., 2 to 3 mA) to result in a deterioration in signal characteristics.
It is therefore an object of the present invention to provide a laser diode module which can perform high-precision temperature control of the LD.
In accordance with the present invention, there is provided a laser diode module comprising a housing; a thermoelectric cooling element having a first surface and a second surface, the first surface being in close contact with an inner surface of the housing, for performing heat exchange between the first surface and the second surface according to a control current supplied; a base provided on the second surface in close contact therewith; a laser carrier and a thermistor carrier both provided on the base in close contact therewith; a laser diode and a thermistor provided on the laser carrier and the thermistor carrier in close contact therewith, respectively; and means for thermally connecting a portion of the base in the vicinity of the laser carrier to the housing.
In the present invention, the provision of the means for thermally connecting a portion of the base in the vicinity of the laser carrier to the housing facilitates the conformity of the temperatures of the thermistor and the laser diode, thereby allowing high-precision temperature control of the laser diode.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will West be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.